1. Field of the Invention
The present invention is directed to saturated, cross-linking compositions and a process for their preparation and more particularly, to compositions useful as binders for powder coatings which produce a coating film with a mat and/or satin surface.
2. Description of the Prior Art
It is known in the coatings industry that saturated compositions in the powder form may be used as coatings. Such compositions require a binder which consists of a reactive resin associated with a cross-linking agent and possibly other well known additives, such as fillers, pigments, etc. These compositions generally produce, after fusion and cross-linking, smooth and glossy coatings with high mechanical and chemical properties. However, recently there has been increasing demands in the coatings industry for compositions capable of producing, after curing, non-glossy, mat and/or satin surfaces. One known process for achieving such a result generally comprises the inclusion in the composition of at least one mineral filler having a grain size distribution chosen to achieve the effect desired. These fillers are included in addition to the conventional pigmented fillers. Unfortunately, this process exhibits a number of major disadvantages, including a high filler content which is detrimental to satisfactory spreading of the binder and capable of causing a lack of cohesion in the coating film, poor mechanical properties, pronounced defects of adherence, and mediocre resistance to solvents and aging.
German Pat. No. 2,351,176 describes a powder coating composition based on a saturated, thermoplastic polyester resin containing cellulose ester particles intended to yield, upon fusion, coatings exhibiting mat and textured surfaces. This composition, however, is not cross-linked, and requires elevated curing temperatures. Moreover, due to the high cellulose ester content, the resulting coating is quite susceptible to degradation by conventional solvents. Accordingly, there exists a need in the art for compositions useful as binders for powder coatings which produce cross-linked coatings with non-glossy surfaces without the disadvantages and inadequacies of presently available compositions.